This invention relates generally to systems for measuring component gases of a sample gas mixture, and more particularly, to a system which compensates for variations in the concentration of component gases in the sample gas mixture.
Infrared absorption gas analyzers operate utilizing a physical property of gases in which the different atomic structures of different gases absorb corresponding spectral regions of infrared radiation. Such absorption of infrared energy by gas contained within a predetermined volume causes a measurable increase in its temperature and pressure. The concentrations of predetermined gaseous components within a gas mixture can be determined from measurements responsive to temperature and pressure.
A typical prior art system for obtaining the desired measurements utilizes a source of infrared radiation which transmits electromagnetic energy along two ray paths; a measuring ray path and a reference ray path. A measuring cell having a generally tubular configuration is disposed with respect to the source of infrared radiation so as to permit the reference ray and measuring ray to pass therethrough. The measuring cell has an inlet and an outlet so as to permit the sample gas to flow therethrough. The system further contains a selectivity cell which is filled with the particular gas component which is desired to be measured, the selectivity cell being disposed in the path of the reference ray. A gas-filled compensation cell is provided in the path of the measuring ray. Finally, at least one detector is provided for converting the relative beam attenuations, as a result of energy absorption in the ray path, into a differential signal which corresponds to the concentration of the particular gas component in the sample gas.
If the sample gas which is to be examined contains, in addition to non-absorbing gas components, several infrared absorbing gas components, the spectral regions of the absorbed energy by the infrared absorbing gas components may be close together or overlap. It is desirable to reduce, and preferably eliminate, the effects of the gas components which interfere with the selective measurement of the particular gas component of interest. One prior art technique for reducing such interference requires filling the compensation cell, which is arranged in the measuring ray path and which contains the particular gas components to be measured, with an additional gas mixture containing a neutral gas, and the interfering component or components in a predetermined concentration. The spectral band overlap of the interfering component and the components to be measured in the selectivity cell is compensated to a degree by the spectral absorption in the compensation cell. It is a problem with this system, however, that if the content of the interfering gas component in the sample gas which is conducted through the measuring cell varies to a substantial extent, the effectiveness of the compensation also varies.
It is, therefore, an object of this invention to provide an improved infrared gas analyzer which compensates for variations in the concentrations of interfering gas components in the sample gas.